1. Field of the Invention
The present invention relates to a liquid crystal display apparatus utilizing an oblique electric field.
2. Description of the Related Art
A TN-type liquid crystal display apparatus is widely used, for example, as a display unit of a personal computer. The TN-type liquid crystal display apparatus, however, harbors the problem that the contrast thereof is reduced or the brightness is reversed when the screen thereof is viewed obliquely. Thus, there is a high demand for a liquid crystal display apparatus in which the contrast is not reduced when it is viewed obliquely.
Japanese Unexamined Patent Publications No. 10-153782 and No. 10-186351, for example, disclose a liquid crystal display apparatus of an IPS (in-plane switching) type in which the contrast thereof is not reduced when it is viewed obliquely. In the IPS-type liquid crystal display apparatus, the liquid crystal is arranged between a pair of substrates, and one of the substrates has a first electrode and a second electrode between which a voltage is applied. The other substrate has no electrode. Therefore, a transverse electric field is formed in a direction substantially parallel to the substrate surface between the first electrode and the second electrode. The liquid crystal is driven by this transverse electric field. The liquid crystal display apparatus disclosed in the above publications uses a liquid crystal of a vertical alignment type having a positive dielectric anisotropy. The liquid crystal molecules are aligned in the direction perpendicular to the substrate surface when no voltage is applied thereto and are aligned in the direction parallel to the transverse electric field when a voltage is applied thereto.
In the IPS-type liquid crystal display apparatus described above, the first and second electrodes are formed of metal stripes extending in parallel to each other on one of the substrates. Upon application of a voltage, electric lines of force of the transverse electric field arcuately extend from the first electrode toward the second electrode. Assuming that the first electrode is located on the left side of the second electrode, the liquid crystal molecules located in the vicinity of the first electrode are aligned upward to the right along electric lines of force, while the liquid crystal molecules located in the vicinity of the second electrode are aligned upward to the left along electric lines of force. The liquid crystal molecules located intermediate between the first electrode and the second electrode are aligned in a direction parallel to the substrate surface along electric lines of force.
The liquid crystal molecules located intermediate between the first electrode and the second electrode, however, are affected by the liquid crystal molecules aligned upward to the left and the liquid crystal molecules aligned upward to the right, and cannot be smoothly aligned in the direction parallel to the substrate surface. This unstable alignment causes disclination. As a result, a black line is generated intermediate between the first electrode and the second electrode, thereby reducing the transmittance. The disclination appears or disappears depending on the voltage or on disturbances, and poses the problem of causing an irregular display or an after image.